How come my stock calendar notifications no longer work?

[AC Question]

I've had my HTC One M8 for about 6 months now and have been using the stock calendar for my appointments but lately there is no notification sound or pop up when I have a reminder set In the calendar. It doesn't make any sound and there is also no notification on the screen or in the status bar at the top. I haven't changed anything in the settings from first set up, it just seemed to happen out of the blue. Any help would be appreciated..Thanks

 

[B. Diddy]

Welcome to Android Central! Have you already double-checked the notification settings in the Calendar app's settings menu? Also, go to Settings>App Manager>All, select Calendar, and make sure the "Show Notifications" box is checked on.